1. Field of the Invention
This invention relates to apparatus and method for controlling fuel injection of a direct injection gasoline internal combustion engine, and particularly to a correction control for injection pulse widths during an increasing change of fuel pressure just after starting of the engine.
2. Related Art of the Invention
There has been known a direct injection internal combustion engine in which a fuel is directly injected into a combustion chamber.
In such a direct injection internal combustion engine, the fuel feeding system comprises an engine-driven high-pressure fuel pump for feeding fuel to a fuel injection valve, an electric low-pressure fuel pump for feeding fuel to the high-pressure fuel pump, a low-pressure pressure regulator for regulating a pressure within a low pressure fuel system between the low-pressure fuel pump and high-pressure fuel pump to a predetermined low pressure, and a high-pressure pressure regulator for regulating a pressure within a high pressure fuel system on a downstream side of the high-pressure fuel pump to a predetermined high pressure (such as disclosed in Japanese Unexamined Patent Publication No. 7-77119).
If a pressure of fuel to be fed to the fuel injection valve (hereinafter called "fuel pressure") deviates from a desired pressure, the quantity of fuel to be actually injected into the fuel injection valve changes with respect to pulse widths of an injection pulse signal supplied to the fuel injection valve (hereinafter called "fuel injection pulse width"), resulting in deterioration of precision in air fuel ratio control. Thus, it is required to provide a sensor for detecting the fuel pressure to thereby correct the fuel injection pulse widths in response to a fuel pressure detected by such a fuel pressure sensor.
Unfortunately, as general characteristics of sensors for detecting fuel pressure, the error ratios become larger as the fuel pressure decreases. As a result, the errors in correcting the fuel injection pulse widths become larger during a low pressure state just after starting. Thus, the precision in air-fuel ratio control may be rather deteriorated, if the fuel injection pulse widths are corrected based on the detected result of the fuel pressure under such a condition.